It’s likely because it’s more economical for them to keep your broken watch and strip it down/recycle it for parts, than it is to source and fit individual parts for repair, given that the numbers coming in for repair are likely very low for something like this.
Given that no data is stored on the watch, I really don’t see what the problem would be to having a new/refurbished one if yours broke within warranty.
Also, these are a budget product. You have to bear that in mind, and not expect the same level of aftercare as you would a more expensive brand/product.
